If so, Theresa May has “swallowed something designed [by the ERG] to be indigestible” - and has thus shown herself to have become their hostage.

Her Chequers Brexit deal seems to be history only days after the ink on its associated white paper has dried: it is difficult to see the EU agreeing to levy the UK's tariffs, as the ERG amendment demands; and absent that implausible agreement from the EU, there is no longer a credible customs plan that would keep open the border between Northern Ireland and the Republic (or at least not one that the EU would recognise).

This implies the UK no longer has a credible plan for its future trading relationship with the EU.